1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to a system and a method for removing the periodic component of the timing mark position error of a self-servo write pattern.
2. Description of the Related Art
FIG. 1 shows an exemplary hard disk drive (HDD) 100 having a recording slider that includes, for example, an offset head 101, that is positioned over a selected track on a magnetic disk 102 using a servo system for writing data to and/or reading data from disk 102. Data is recorded in arrays of concentric data information tracks on the surface of disk 102. While HDD 100 shows only a single magnetic disk 102, HDDs typically have a plurality of stacked, commonly rotated rigid magnetic disks. The servo system of HDD 100 can include an actuator 105, a voice-coil motor (VCM) 104, for coarse positioning a read/write head suspension 106, and a secondary actuator, such as a microactuator or micropositioner, for fine positioning read/write head 101 over a selected track. As used herein, a microactuator (or a micropositioner) is a small actuator that is placed between a suspension and a slider and moves the slider relative to the suspension.
Conventional self-servo writing is basically performed one track at a time from the inner diameter (ID) to the outer diameter (OD) of a magnetic recording disk, such as disk 102, using a spindle motor index and information from previously written nearby tracks. The magneto-resistive (MR) read sensor and the write element are offset from each other on offset head 101 and, consequently, are not on same radius, particularly toward OD of the disk. Accordingly, the offset between the read sensor and the write element changes with respect to tracks on the disk as the skew angle of the armature changes. For example, near the ID of the disk, the offset between the read sensor and the write element typically is a distance of about eight tracks. At the OD of the disk, the offset between the read sensor and the write element typically is a distance of about 40 tracks. The offset difference with respect to the disk is further exacerbated by variations in the read/write head dimensions and track densities between different models of disk drives and the variations between “identical” parts for the same model of disk drives.
Ideally, a self-servo pattern should be a line nominally following the arc of motion of the head from the ID to the OD of the disk, but because self-servo writing is basically performed by writing the servo pattern one track at a time and because of the offset between the read sensor and the write element, errors propagate through the servo pattern that cause the servo pattern to be warped away from the desired trajectory (which is nominally straight locally). One error pattern that propagates through the self-servo pattern from the ID to the OD of a disk has a period that is related to the offset distance between the read sensor and the write element. To further complicate matters, the periodic error pattern changes as the skew angle of the armature changes. Thus, the warp can become large enough to cause a low-amplitude misalignment or missed windows during a high-speed seek.
Consequently, what is needed is a technique to determine and remove the periodic component of the timing mark position error of a self-servo write pattern.